One gearing structure that provides superior common normal, rolling contact and low friction attributes during force transfer is a sprocket and roller system, wherein solid sprocket gear teeth engage roller elements (e.g. on a roller chain, or a plurality of rollers arrayed and attached to another gear element such as a disc, cylinder, etc.). Such systems have many economic and design advantages. Frictional problems are minimized by the rolling interaction of rollers with respect to interfacing sprocket gear teeth, and many lubrication options are possible. A well known chain and sprocket system for variable speed reduction and torque transmission is a bicycle “derailleur” system, where speed and torque outputs are chosen by selecting from a group of input and output sprocket gears sharing a common chain.
In the interaction of gear elements driven by gear teeth in speed reduction and torque transmission, it is desirable to have a common normal orientation of the respective contacting surfaces intersecting a line of centers at all times, a fundamental principle sometimes known as the “common normal” principle. Gear profiles that do not satisfy this principle may not have a constant angular velocity ratio. A driving first gear may revolve at a constant rate (RPM), but a failure to maintain the common normal during the entire interaction with a driven gear contact element results in varying output revolution rate and torque transmission behavior. The driven gear may speed up and slow down instead of rotating smoothly and constantly responsive to a constant rotational input of the first gear.
Planetary power transmission composite gear structures are known for torque and speed reduction and increasing applications. Rotation of a circular “sun” gear about its central axis with rotation speed and torque engages one more “planetary” gearing element(s) disposed about the sun gear, wherein if more than one planetary gear is provided, said planetary gears are generally arrayed about the sun gear central axis. The planetary gears in turn responsively engage a “ring” gear disposed about the sun gear and the planetary gears generally arrayed about the sun gear central axis. In application, a rotational motion input through one of the ring gear and sun gear elements is translated through the planetary gearing element(s) into a rotational motion output by the other of the sun and ring gears at either an increased speed and reduced torque or a reduced speed and increased torque output.
The performance capabilities of sprocket-and-roller planetary systems may be limited relative to other systems, such as meshed fixed tooth systems. In one aspect, the overall strength, force bearing or force transmission capacity of a prior art sprocket-and-roller planetary system may be lower than comparably sized meshed fixed tooth systems.